Maintaining a normal biological makeup and functional status during sleep is believed very important in medical community. For example, when sleeping on one's back, if the pillow is too high, the normal bending of cervical vertebra will disappear, and the cervical vertebra will distort to an opposite direction. Accompanying the distort of cervical vertebra, the windpipe, blood vessel, muscle and ligament in the neck will all distort; the root of tongue will drop back to block air duct, so as to cause snoring and even SAS (sleep apnea syndromes). Sleeping on one's back for eight hours a day will cause many kinds of disease.
Except sleeping on one's back, one may sleep on one's left side or right side. The pillow is too high or too low is most common problem, when one sleeps on one's side, which will cause severe distortion of cervical vertebra and upper thoracic vertebra, and will cause the distortion of windpipe, blood vessel, muscle and ligament in the neck. And in this circumstance, the weight of the head and neck is mostly on the shoulder, which will cause the overstress of the shoulder and obvious displacement of the shoulder blade. Sleeping in this manner for too long will cause all kinds of disease on the neck, shoulder and back.
Besides the “decubitus” problem the medics is familiar with, maintaining one sleeping posture for a long time, especially on one's side, even if this posture is biological and functional, will cause damage to the health. The above-mentioned opinions are widely acknowledged and paid attention around the globe. Mr. Xigu from Japan described this theory in detail in his book Xigu therapy (Xigu Gongliang, The People's Medical Publishing House, 1986). He believes in this book that sleeping on the left side may cause heart disease, diarrhea, and so on; sleeping on the right side may cause respiratory disease, obstipation, and so on, and may have uneven leg length, uneven shoulder height, lateral curvature, inclination of pelvis, and so on at same time. Chiropractors of European and American schools also identify and take this problem seriously.
In order to maintain a normal biological makeup and functional status of human body, especially of neck, shoulder and back, during sleep, the sleeper should use low pillow or no pillow when sleeping on the back, and use high pillow when sleeping on the side; the sleeper should also ensure the time of sleeping on the left side approximately equal to the time of sleeping on the right side, and avoid sleeping in only one posture for a long time. As the requirement for the height of the pillow when people sleeping on the back and side is quite opposite, the pillow that conforms the biological structure should distinguish the supine recumbency pillow and lateral recumbency pillow.
Further, the skull of human is in ellipse shape, so when sleeping on the back, it is very hard to keep skull upright, and the skull will incline to one side and always to only one side. This will cause the twist of the cervical vertebra and imbalance growth of the skull due to asymmetry effect, which will lead to oblique of the skull (including the five organs in the face). In order to solve this problem, the skull should be fixed when lying on the back to avoid inclination.
When people sleeping on the back, the weight of the neck will make the cervical vertebra dropping down to bed so as to decrease the curvature thereof, so that people should use a column pillow to support the middle part of the cervical vertebra (It is meaningless to support the whole cervical vertebra) to cancel the weight of the neck and maintain the curvature of the cervical vertebra.
It is also not right to use pure high pillow when people sleeps on the side. Because the shoulder is wider than the wrist, when people sleeps on the side, the spine is not parallel with the bed, an angle is formed therebetween, and the spine near neck is higher than the spine near wrist. When people sleeps on the side, the slant angle of the spine is the angle between the spine and the projection line thereof to the bed, which is somewhere between 5 and 25. In order to comply with the slant angle of the spine, the surface of the side sleep pillow should incline forwardly to make a “spine complying angle”, which is equal to the slant angle of the spine (about 5 to 25), so as to avoid the spine, especially cervical vertebra to distort.
When people sleep on the side, people intend to sleep on the side excessively. The reason is that when people sleeps on the side, people are used to put the arm and leg on one side in front of the body, which will drag the body to twist forward, so as lead to excessive side sleep. In this posture, the harm is obvious. Not only the heart and lung are stressed, but also the shoulder contacting to the bed is excessively stressed and the shoulder joint is excessively folded inwardly, which will cause a chronic damage of the joints around the shoulder and soft tissue, block of blood circulation in upper limb, and damage to nerves in upper limb. In order to correct excessive side sleep, the side sleep pillow should have a “mechanism inhibit too great an angle of lateral tilt”, which made an angle ranging from 0 to 15, to adjust the side sleep amplitude of the head, so that the face of sleeper slightly bends backwardly to effectively restrain the excessive side sleep of the whole body and to avoid the head of sleeper falling backwardly and downwardly along the surface of the side sleep pillow.
When people rolls over from the back sleep to side sleep, one must bend one's pelvispelviccoxa and knees, so the knees are lifted in front of the body. According to the “reaction principle”, people will move the hip backward unconsciously to keep balance so as to avoid falling down from bed, so that an angle is formed in a horizontal plane between the upper body (spine) and longitudinal axis of the bed, which is about 0 to 20 degree, and can be called as rolling angle. Therefore, the rolling angle is an angle between the projection line of spine to the bed when sleeper sleeping on the side and the projection line of spine to the bed when sleeper sleeping on the back, presented as a sharp angle. In order to comply with this angle, there should be a “rolling complying angle” between the back sleep pillow and side sleep pillow, which is an angle between the projection of longitudinal axis of side sleep pillow and back sleep pillow to a horizontal plane, and also can be described as an angle between the projection of inner edge of side sleep pillow and outer edge back sleep pillow to the horizontal plane. The rolling complying angle is equal to the rolling angle, which is about 0 to 20. The rolling complying angle enables the upper body (spine) vertical to the pillow (in a horizontal plane) during side sleep and the shoulder near the bed closely to the pillow, so as to avoid the head away from the pillow and hanging in the air.
When people sleeps on the side, some people with shorter neck, or with shrugged shoulder, can only lay the upper part of head on the pillow and will uncomfortable hang lower part of his head in the air, due to the slant angle of the spine, because his shoulder near bed is against the pillow. In order to solve this problem, it is necessary to enlarge the space between the shoulder near bed and the side sleep pillow so as to receive the over high shoulder and increase the contact area of the surface of side sleep pillow and the head so as to fully support the head.
Therefore, in order to conform to the biological structure no matter during side sleep and back sleep, it is necessary to distinguish the back sleep pillow and side sleep pillow, so as to avoid inclination of the head, comply with the slant angle of the spine during side sleep, and correct excessive side sleep. Further, a rolling complying angle should be provided to avoid head being away from pillow when turning over the body, the space between the shoulder and side sleep pillow should be enlarged, and the contact area of the surface of side sleep pillow and the head.
For the sake of illustration, “front”, “back”, “left”, “right”, “up”, and “down” refer to the direction of the standing object.
A Chinese patent entitled Adjustable combined cervical vertebra pillow (Publication number CN1188627A) comprises a unit freely combined by a neck pillow, back sleep pillow, right lateral recumbency pillow and left lateral recumbency pillow, and an outside pillowslip. The back head pillow and the neck pillow in front thereof constitute a middle part of adjustable combined cervical vertebra pillow, for back sleep. The right lateral recumbency pillow is on the right of the middle part, for right side sleep. The left lateral recumbency pillow is on the left of the middle part, for left side sleep. The back head pillow, right lateral recumbency pillow and left lateral recumbency pillow are all composed by a stack of rectangular soft slices tied via a nylon fastener tape. Apparently, the height of the back head pillow, right lateral recumbency pillow and left lateral recumbency pillow can be adjusted by the number of the slice. The middle part is higher than the left and right side. The neck pillow is in column shape and transversely placed. It composed by curling a rectangular soft slice and fastened via a nylon fastener tape. The size can be adjusted by the number of the slices. The drawback is that it can only adjust the height of the back head pillow, left pillow and right pillow.
Further, a Chinese patent entitled Functional pillow with adjustable height (Publication number CN2930492Y) comprises an upper pillow panel, screw, inner gear sleeve, outer gear sleeve, and lower pillow panel; the lower surface of the upper pillow panel connects to the top of the inner gear sleeve, the outer gear sleeve engages with the screw, and the seat for fixing the screw is fastened with the lower surface of the lower pillow panel. The height of the Functional pillow with adjustable height can be adjusted by spinning the screw. The pillow inlet is of S-shape, and put on the entire upper pillow panel. It has the advantage of adjustable height, and adjustable slant angle of the upper pillow surface. However, the drawback is that there is no difference between the back sleep pillow and side sleep pillow when adjusting the height and slant angle, and the range of adjusting angle is only from 0 to 6, which is very small, so that the problem brought by slant angle of spine during side sleep can not be solved. Further, it is not considered that when sleeper turns back sleep to left or right side sleep, the head cannot fully contact with pillow, and it is not considered how to prevent excessive side sleep.